Apparatus for coating filamentary material

ABSTRACT

Method and apparatus for coating fibers of glass and the like with a liquid such as molten aluminum. The fibers are passed through a lip of the molten metal which projects from an upper edge of a vessel which holds a body of the molten metal. The coated fibers are then passed over a heated wiper to more uniformly distribute the molten metal on the fibers before the metal hardens. An automatic control is provided for maintaining a substantially constant molten metal level in the vessel as the metal is applied to the fibers.

United States Patent 1191 Kime [111 3 ,831,551 [451 Aug. 27, 1974 1APPARATUS FOR COATING FILAMENTARY MATERIAL [75] Inventor: Roger A. Kime,Napoleon, Ohio [73] Assignee: Owens-Corning Fiberglas Corporation,Toledo, Ohio 22 Filed: Apr. 14,1972

21 Appl. No.: 244,182

[52] US. Cl 118/7,118/101, 118/420 [51] Int. Cl. B05c 11/10 [58] Fieldof Search 118/7, 8, 419, 420, 101, 118/D1G. 19, DIG. 22; 117/114 R, 114A, 114B, 114 C, 115

[56] References Cited UNITED STATES PATENTS 2,963,739 12/1960 Whitehurstet a1. 118/401 X 2,976,177 3/1961 Warthen 118/420 X 3,086,889 4/1963Strong 118/7 UX 3,227,577 H1966 Baessler et al 118/420 X 3,251,7105/1966 Taylor et a1. 118/7 X 3,510,345 5/1970 Marchant 118/7 X 3,522,8368/1970 King 118/401 X 3,538,884 1l/1970 Carreker, Jr. et a1. 1113/?3,632,700 l/1972 Oglevee 118/7 X 3,671,298 6/1972 Maynard... 118/419 X3,749,057 7/1973 Garick 118/420 Primary Examiner-Morris Kaplan A n yAgent, or Firm-Staelin & Overman;

Oliver E. Todd, Jr.

[57] ABSTRACT Method and apparatus for coating fibers of glass and thelike with a liquid such as molten aluminum. The fibers are passedthrough a lip of the molten metal which projects from an upper edge of avessel which holds a body of the molten metal. The coated fibers arethen passed over a heated wiper to more uniformly distribute the moltenmetal on the fibers before the metal hardens. An automatic control isprovided for maintaining a substantially constant molten metal level inthe vessel as the metal is. applied to the fibers.

9 Claims, 5 Drawing Figures PATENILM 3,831,551

SIEH -1 BF 2 FE-l- Tmz BACKGROUND OF THE INVENTION This inventionrelates to fiber production and, more particularly, to an improvedmethod and apparatus for coating fibers with a liquid. In a preferredform, glass fibers are coated with molten aluminum.

Radio wave reflectors consisting of random length electrical conductorsare sometimes dispersed from military aircraft to confuse enemy radarand to misdirect anti-aircraft fire controlled thereby. Such reflectorsare commonly known "as chaff, rope or window. The effectiveness of chaffagainst enemy radar depends upon a number of factors. While heaviermetals such as zinc, tin, lead, bismuth and some alloys of these metals,such as copper and nickel, may theoretically be used in manufacturingchaff, in actual practice aluminumhas been the metal chiefly employedbecause of its low specific gravity and its resulting capacity ofrelatively slow descent through the air. Another factor is the effectivelength of the chaff with respect to the frequency of the enemy radar.Since individual lengths or strips of chaff act as dipoles which reflector re-radiate the radar waves incident thereon, greatest effectivenessrequires a length closely equal to one-half the wavelength of thehostile radar.

Furthermore, it is necessary that the individual lengths or strands ofchaff be sufficiently stiff to resist bending without breaking, andsufficiently resilient to assume or to reassume a linear form.Otherwise, if the individual lengths of chaff are easily distorted outof a linear form, as by air currents, or if they become easily entangledwith one or more other strands on being launched or expelled from anaircraft, the effectiveness of the chaff in re-radiating or reflectingthe radar waves, and thereby confusing enemy fire, can be greatlydiminished.

In a preferred form, chaff has been formed from random lengths of glassfibers coated with an electrical conductor, preferably aluminum. Chaffof this type has been particularly effective due to the strength andresilience of the glass fibers. Even when the glass fibers are severalfeet long, they may be made ofa suitable diameter to impart sufficientresilience for assuming a linear form.

Aluminum coated glass fibers have other potential commercial uses.Aluminum wire, for example, is generally used for high voltage powertransmission. The substitution of aluminum coated glass fibers for thealuminum wire would result in a considerable savings in the cost ofmaterials used for manufacturing power transmission lines. Furthermore,the aluminum coated glass fibers would not stretch as annealed aluminumwire stretches.

Various methods have been used in the past for manufacturing aluminumcoated fibers. One such method is shown in U.S. Pat. No. 3,544,997wherein glass fibers are passed over a roll applicator which appliesmolten metal to the fibers. However, problems have occurred with thisand other prior art methods. Extreme care must be taken as molten metalis applied to the glass fibers to prevent thermal stress in the glassfibers and to prevent the metal from freezing or solidifying too soon,causing the fibers to break. If the molten aluminum collects on theapplicator, it acts as a heat sink and increases the probability thatthe aluminum will solidify and break the fibers.

SUMMARY OF THE INVENTION According to the present invention, an improvedapparatus is provided for coating fibers of glass, synthetic resins, andthe like with molten metal and other liquids. After the fibers areformed, and while they are still quite hot, the fibers are passedthrough a lip of the mo]- ten metal projecting from an upper edge of avessel which holds a body of the molten metal. The fibers are thenpassed over a heated wiper to distribute the molten metal uniformly overthe fibers. The fibers are then cooled, a sizing is applied and thecoated fibers are collected into a suitable package.

The level of the molten aluminum in the vessel is extremely critical formaintaining a constant and uniform lip for uniformly coating the fibers.The level of the molten aluminum is sensed by means of a pneumaticprobe. A wire formed of the metal from which the fibers are coated iscontinuously fed into the vessel at a relatively, slow rate when thesurface of the molten metal exceeds a desired level and :at a fast ratewhen the surface of the molten metal is below the desired level. A levelcontrol circuit is responsive to the pneumatic probe for controlling thewire feed rate. By changing the rate at which the wire is fed into thevessel, an average feed rate corresponding to the rate at which themetal is applied to the fibers is maintained. The level control circuitalso includes a safety disconnect for stopping the wire feed andenergizing an alarm when the surface of the molten metal is eitherdangerously high or dangerously low. If the molten metal level shoulddrop from a dangerously high level to within an allowed tolerance, thewire feed may be automatically reinitiated either immediately or after ashort time delay.

Accordingly, it is a preferred object of the invention to provide animproved apparatus for coating fibers with metal.

Another object of the invention is to provide an improved apparatus forproducing aluminum coated glass fibers.

Still another object of 'the invention isto provide improved apparatusfor maintaining a substantially constant molten metal level in apparatusfor applyingmolten metal to fibers.

Other objects and advantages of the invention will become apparent fromthe following detailed description, with reference being made to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic frontelevational view of apparatus in accordance with the present inventionfor pro- FIG. 4 is an enlarged fragmentary view showing the constructionof the upper edge of the vessel for holding the moltenmetaland theformation of a molten metal lip; and

FIG. 5 is a schematic diagram of the electric circuit for maintainingsubstantially constant the level of the molten metal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2,apparatus embodying the principles of the present invention is shown forproducing aluminum coated glass fibers. Although a specific embodimentis shown and described, it will, of course, be appreciated that theapparatus 10 may be used for coating glass fibers with liquids andmetals other than aluminum and'for coating other types of fibers withliquids such as molten metals. The apparatus 10 may include conventionalapparatus for forming glass fibers such as a melting unit 11 havingassociated therewith an electrical feeder or bushing 12. The bushing 12has in its bottom a plurality of aligned tips 13 having aligned orificesof small dimension which form the streams of molten glass from whichfibers 14 are drawn or attenuated at a high velocity. The bushing 12 ismade of a high temperature electrically conducting material such asplatinum and is provided with terminals 15 at opposite ends thereofacross which a potential is applied to supply current of a magnitudesufficient to heat the molten glass to the desired attenuatingtemperature.

The force of withdrawal of the fibers 14 from the molten materialflowing from the bushing 12 may be provided by conventional windingapparatus, such as a winder 16. The winder 16 includes a motor (notshown) for driving a collet 17. A package tube 18 is placed on thedriven collet 17. The fibers 14 may be individually wound on the packagetube 18, as shown, or they may be gathered into a single strand andwound on the package tube 18. When the fibers 14 are collected into asingle strand, a traverse must be provided to distribute the stranduniformly across the package 18.

Immediately after the streams of molten glass are attenuated into thefilaments or fibers 14, the fibers 14 pass a vessel 19 where they areindividually coated with molten aluminum. The vessel 19 is preferably ofa silicon nitride ceramic which is not attacked by molten aluminum. Thevessel 19 must be positioned sufficiently close to the bushing tips 13that the fibers 14 are still hot when they are coatedwith the moltenaluminum. A shield (not shown) may also be positioned between the fibers14 adjacent the tips 13 to control the temperature uniformity of thetips 13 and of the molten glass streams emitted from the tips 13, tothereby control the uniformity of the diameter of the plurality offibers 14. If the spacing between the bushing tips 13 and the vessel 19is such that the fibers 14 have cooled appreciably, the fibers 14 aresubject to a severe thermal shock when they are coated with the moltenaluminum. Such a thermal shock may cause the fibers 14 to break. Aspacing on the order of three or four inches between the bushing tips 13and the application of the molten aluminum, for example, has been foundsatisfactory.

After the coated fibers 14 have cooled and the aluminum coating hashardened, the fibers 14 are drawn over an applicator roll 20 on a sizingapplicator 21 where a suitable sizing, such as a dilute stearic acidsolution, is applied to the fibers. The fibers are subsequentlycollected by the winder 16 on the package tube 18.

As the fibers 14 are coated with the molten aluminum, the aluminum levelin the vessel 19 will tend to drop. Additional aluminum is supplied tothe vessel 19 to maintain the molten aluminum level in the vessel 19substantially constant. The additional aluminum is supplied in the formof wire 22 delivered from a spool or reel 23. An electric motor 24operates a suitable drive mechanism 25 for forcing wire from the spool23 through a tube 26. The tube 26 guides the aluminum wire into thevessel 19. The aluminum in the vessel 19 is maintained in a moltenstate, and the added aluminum wire 22 is continuously melted, by meansof an oven 27 which surrounds the vessel 19. The oven 27 may consist ofastainless steel box lined with a suitable high temperature refractorymaterial. A coating, such as aluminum oxide, is applied to the stainlesssteel box to prevent corrosion from molten aluminum which may come intocontact with the box. A plurality of electrical resistance heaters 27aare located within the oven 27 for supplying heat to the vessel 19. Theheaters 27a may be arranged for zone heatings to maintain the moltenaluminum at a substantially uniform temperature across the vessel 19.

The rate at which the aluminum wire 22 is supplied to the vessel 19 iscontrolled by a level control circuit 28 which senses the level of themolten aluminum within the vessel 19 by means of a pneumatic probe 29.The level control 28, as will be discussed in greater detail below,controls the operation of the motor 24 for feeding the wire 22 into thevessel 19 at the appropriate rate.

Referring now to FIGS. 3 and 4, the pot or vessel 19 for holding themolten aluminum or other coating liquid is shown in detail. The vessel19 is filled with aluminum to a desired surface level 30. The pneumaticprobe 29 is positioned above the surface level 30 with an open end ornozzle 31 spaced slightly above and directed toward the surface level30. Except for one side 33 of the vessel 19, an upper edge 34 of thevessel 19 extends above the maximum level of the molten aluminum.

The upper portion of the vessel side 33 is shown in detail in thefragmentary view of FIG. 4. The side 33 includes an upper edge 35 whichis spaced below the desired aluminum surface level 30. A weir or dam 36projects upwardly from the upper edge 35 towards the surface 30. The dam36 has an uppermost edge 37 which is parallel to and spaced slightlybelow the desired surface level 30. The uppermost edge 37 may be eitherrounded as shown or pointed, although a rounded edge is easier tomanufacture. From the dam 36, the upper edge 35 of the side 33 extendsoutwardly to an exterior edge 38. The exterior edge 38 must be straightand parallel to the molten aluminum surface 30 and parallel to theuppermost edge 37 of the dam 36. When the vessel 19 is filled withmolten aluminum to the normal or desired surface level 30, the moltenaluminum flows over the dam 36 and, through surface tension, forms a lip39 which projects outwardly from the exterior edge 38. The lip 39 willbe maintained by the dam 36, even though the molten aluminum in thevessel 19 momentarily drops below the upper edge 37 of the darn 36.

So long as the molten aluminum is maintained at substantially thedesired level 30, surface tension will prevent the aluminum from flowingover the exterior edge 38. The flow of molten aluminum is furtherprevented by the formation of a concave surface tension recess 40 withinthe vessel side 33 contiguous to the exterior edge 38. lmmediately belowthe surface tension recess 40, a second recess 41 is formed in thevessel side 33. A small diameter ceramic rod 42 is mounted within therecess 41. An electric heater wire 43 is passed longitudinally throughthe ceramic rod 42 for electrically heating the rod 42. Electric currentis passed through the wire 43 to heat the rod 42 to above the meltingtemperature of aluminum.

After the molten stream of glass from the bushing tip 13 is attenuatedinto a fiber 14 and before the fiber 14 has cooled appreciably, thefiber 14 is passed through the molten aluminum lip 39 projecting fromthe vessel side 33. In passing through the aluminum lip 39, the fiber 14is at least partially coated with the molten aluminum. The coated fiberis then wiped over the ceramic rod 42 which spreads the molten aluminumover the fiber 14, increasing the probability that the fiber 14 will be100 percent coated with aluminum. As previously discussed, the coatedfiber 14 is subsequently cooled, sizing is applied to the fiber 14 andthe fiber 14 is wound onto a package tube 18. It has been found thatwhen the fiber 14 is 100% coated with aluminum, it will have a dullappearance. If less than 100 percent of the surface area of the fiber 14is coated with the aluminum, the coated fiber 14 will appear shiny.Thus, a visual examination will readily indicate when the apparatus isproperly adjusted for completely coating the fibers with the moltenaluminum.

It has been found that the construction and the alignment of the vessel19 is extremely critical for obtaining 21 I00 percent aluminum coatingand for minimizing fiber breakage. If the uppermost edge 37 of the dam36 is not flat and aligned parallel to the molten aluminum surface or ifthe exterior edge 38 of the side 33 is not straight and parallel'to themolten aluminum surface and parallel to the edge 37, then the lip 39will not extend uniformly across the full width of the vessel 19. Inextreme cases, the molten aluminum will flow over the side 33 withoutforming a lip 39. lf the lip 39 is not uniform and some of the fibers 14are not coated with the molten aluminum, abrasion and tension caused bydragging the fibers over the ceramic rod 42 will cause the uncoatedfibers 14 to break. In addition, both the exterior edge 38 and theheated rod 42 must be parallel to the aligned plurality of orificed tips13 on the bushing 12.

Another difficulty occurs at times from the aluminum gauging up andfreezing on the ceramic rod 42. The probability of this occurring isgreatly reduced by heating the rod 42. Howeventhis may still occur undercertain circumstances. If the level of the molten aluminum in the vessel19 is appreciably above the desired level 30, the aluminum may eitherflow over the exterior edge 38 onto the rod 42 or the lip 39 may projecttoo far from the edge 38, applying too much aluminum to the fibers 14,which is deposited on the rod 42. As aluminum builds up on the ceramicrod 42, it acts as a heat sink and removes heat from the fibers l4.Eventually, sufficient heat is withdrawn from at least some of thefibers 14 to cause the aluminum to harden and the fibers 14 to break.Another possible cause of aluminum buildup on the ceramic rod 42 is fromnot having the vessel 19 level so that the uppermost edge 37 of the damis not parallel to the surface 30. In this case, either the lip 39 willnot be uniform or the molten aluminum will flow from the vessel 19before the lip 39 is formed.

Referring now to FIGS. 1, 2 and 5, the level control 28 for maintainingthe molten aluminum at substantially the desired level 30 in the vessel19 is shown in detail. As previously stated, a pneumatic probe 29 ispositioned above the vessel 19 with an open end or nozzle 31 spacedimmediately above and directed towards the normal surface level 30. Thenozzle 31 must therefore be constructed from a material which will notbe corroded by molten aluminum, such as aluminum oxide coated stainlesssteel or silicon nitride. A highly regulated constant flow of air orother gas is delivered from a suitable source (not shown) to thepneumatic probe 29. The back pressure within the probe 29 will bedependent upon the level of the molten aluminum within the vessel 19. Asthe molten aluminum level drops from the desired level 30, the backpressure within the pneumatic probe 29 will drop. Conversely, as themolten aluminum level increases above the desired level 30, the backpressure Within the pneumatic probe 29 will increase.

The back pressure within the pneumatic probe 29 is applied to operate anadjustable pressure switch which may, for example, consist of a type3010 HH photohelic pressure switch manufactured by Dwyer InstrumentCompany. As shown in H0. 5, the pressure switch 44 is a double-pole,single-throw switch. The switch 44 is adjusted such that, when themolten aluminum exceeds the desired surface level 30, the back pressurewithin the probe 29 will close the switch 44. When the molten aluminumdrops below the desired level 30, the pressure drop opens the switch 44.

A conventional electrical power source (not shown), such as a commercial1 lO-volt 60 Hz. power source, is connected to a pair of input terminals45 and 46 for operating the level control 28 and the motor 24. The inputterminal 45 is connected through a main on/off power switch 47 to aterminal 48. When the switch 47 is closed to apply power to the terminal48, a pilot light 49 is illuminated. Power is also applied to operatethe motor 24 through a voltage divider consisting of a potentiometer 50connected between the terminals 46 and 48 through normally closedcontacts of a relay 5] and, a pair of series connected pressure switches52 and 53. The potentiometer 50 is set to apply a suitable operatingvoltage to the motor 24 for driving the motor 24 at a predetermined fastrate. When the motor 24 is operated at the fast rate, the aluminum wire22 is supplied to the vessel 19 at a rate faster than the aluminum isapplied to the fibers 14.

As the wire 22 is supplied at a fast rate to the vessel 19, the moltenaluminum level will build up within the vessel 19 until the moltenaluminum exceeds the desired surface level 30. At this point, thepressure switch 44 is closed to simultaneously energize a high levelwarning lamp 54 and the winding of the relay Sll. When the relay 51 isenergized, the motor is connected to receive power from the variable tapof a second potenti ometer 55 and is disconnected from the potentiometer50. The second potentiometer 55 is connected as a voltage dividerbetween the terminals 46 and 48 for applying a lower operating voltageto the motor 24. The second potentiometer 55 is set to operate the motor24 for feeding the aluminum wire 22 into the vessel 19 at a rate slowerthan the molten aluminum is applied to the fibers 14. Thus. in normaloperation, the pressure the desired level 30. As a consequence of theoperation of the switch 44, the average rate at which the aluminum wire22 is supplied to the vessel 19 will equal the rate at which the moltenaluminum is applied to the fibers 14.

Under certain circumstances, the molten aluminum level within the vessel19 may become dangerously high or dangerously low. The pressure switches52 and 53 are also connected to the pneumatic probe 29 for sensing thedangerously high and dangerously low conditions, respectively. Theswitch 52 is set such that it is actuated when the pressure within theprobe 29 increases due to the surface level of the molten aluminumexceeding the desired level 30 by a predetermined small amount. Theswitch 52 should be set such that it is actuated just before the moltenaluminum overflows the vessel 19 to discontinue feeding of additionalaluminum wire 22 into the vessel 19. If the aluminum level shouldsubsequently drop, the switch 52 will be released to again energize themotor 24. An optional time delay circuit (not shown) may be provided sothat a short time interval occurs after the molten aluminum level dropsand before the actuated switch 52 is released. If, for example, severalof the fibers 14 break, the aluminum level within the vessel 19 maybuild up faster than the molten aluminum is applied to the remainingfibers 14, even though the aluminum wire 22 if fed into the vessel 19 atthe slow rate. In this event, the aluminum level will build up until theswitch 52 is actuated to stop the wire feed motor 24. As the moltenaluminum is consumed by the remaining ones of the fibers 14, thealuminum level will drop until the switch 52 is released to turn on themotor 24 and feed additional wire 22 into the vessel 19. Thus, theapparatus will continue to operate without overflowing the vessel 19.

If, on the other hand, the vessel 19 should develop a crack or themolten aluminum level within the vessel 19 should drop appreciably belowthe normal level for any other reason, the switch 53 will be released bya decrease in the pressure within the pneumatic probe 29. When theswitch 53 is released, the motor 24 is stopped to discontinue feedingaluminum wire 22 into the vessel 19. When either the switch 52 isenergized or the switch 53 is released to stop the motor 24 because ofdangerous aluminum levels, a warning lamp 56 is illuminated to notifythe operator of the apparatus 10.

lt will be appreciated that various changes and modifications may bemade in the apparatus 10 without departing from the spirit and the scopeof the claimed invention. The apparatus 10 may, for example, be usedwith other conventional apparatus for forming glass fibers or withapparatus for forming fibers from other materials such as syntheticresins. In addition, the apparatus 10 may be used for coating suchfibers with metals other than aluminum or with other coating materialswhich are in a liquid state.

What I claim is:

1. Apparatus for coating fibers with a material in a liquid statecomprising, in combination, a vessel for holding the liquid material,said vessel having a straight horizontal side portion, and means forsupplying the material to the vessel at a rate for maintaining theliquid material at a desired level just above said side portion, saidmaterial supplying means including means for continuously supplying thematerial to the vessel at a rate faster than the material is normallyapplied to the fibers when the liquid material level is below thedesired level and means for continuously supplying the material to thevessel at a rate slower than the material is normally applied to thefibers when the liquid material level is above the desired levelwhereby, through surface tension, the liquid material defines a lipprolt) jecting from said side portion for coating the fibers when suchfibers are passed through such lip.

2. Apparatus for coating fibers with a material in a liquid state, asset forth in claim 1, and including means positioned below and parallelto such lip of liquid material for wiping the fibers after they arecoated to more uniformly coat the fibers with the liquid material.

3. Apparatus for coating fibers with a material in a liquid state, asset forth in claim 2, and including means for heating the material insaid vessel to maintain the material in a liquid state, and means forheating said wiping means.

4. Apparatus for coating fibers with a material in a liquid state, asset forth in claim 1, and including means for disabling said materialsupplying means when the material in said vessel is above apredetermined dangerously high level, and means for disabling saidmaterial supplying means when the material in said vessel is below apredetermined dangerously low level.

5. Apparatus for coating glass fibers with metal comprising, incombination, a vessel for holding molten metal, means for heating metalin said vessel to 21 molten state, means for supplying metal to saidvessel at an average rate to maintain a desired surface level for themolten metal, said vessel having a wall with an upper edge spaced belowthe desired surface level for the molten metal, a dam extending upwardlyfrom said upper wall edge and spaced inwardly from an exterior edge ofsaid upper wall edge, said dam having an uppermost edge spaced below andparallel to the desired surface level whereby the molten metal can flowover said dam to form a lip projecting from said exterior edge as aconsequence of the surface tension of the molten metal, a ceramic wiperspaced below and parallel to such lip of molten metal, and means forelectrically heating said wiper to above the melting temperature of themetal whereby, when glass fibers are passed through such lip and oversaid wiper, such fibers are coated with the metal.

6. Apparatus for coating glass fibers with metal, as set forth in claim5, wherein said vessel includes a concave surface tension recess formedin said vessel parallel to and adjoining said exterior edge, saidsurface tension recess lying between said exterior edge and said wiperto prevent the molten metal from flowing onto said wiper.

7. Apparatus for coating glass fibers with metal, as set forth in claim6, wherein said means for supplying metal to said vessel includes meansfor continuously feeding wire formed from the metal into said vessel,means for sensing the surface level of the molten metal in said vessel,and means responsive to the sensed surface level for controlling thewire feed rate to maintain the molten metal at substantially the desiredsurface level.

8. Apparatus for coating glass fibers with metal, as set forth in claim7, wherein said control means causes said feed means to feed wire at arate faster than the metal 9. Apparatus for coating glass fibers withmetal, as set forth in claim 8, and including means for disabling saidfeed means when the deviation of the sensed surface level from thedesired surface level exceeds a predetermined tolerance.

l l l

1. Apparatus for coating fibers with a material in a liquid statecomprising, in combination, a vessel for holding the liquid material,said vessel having a straight horizontal side portion, and means forsupplying the material to the vessel at a rate for maintaining theliquid material at a desired level just above said side portion, saidmaterial supplying means including means for continuously supplying thematerial to the vessel at a rate faster than the material is normallyapplied to the fibers when the liquid material level is below thedesired level and means for continuously supplying the material to thevessel at a rate slower than the material is normally applied to thefibers when the liquid material level is above the desired levelwhereby, through surface tension, the liquid material defines a lipprojecting from said side portion for coating the fibers when suchfibers are passed through such lip.
 2. Apparatus for coating fibers witha material in a liquid state, as set forth in claim 1, and includingmeans positioned below and parallel to such lip of liquid material forwiping the fibers after they are coated to more uniformly coat thefibers with the liquid material.
 3. Apparatus for coating fibers with amaterial in a liquid state, as set forth in claim 2, and including meansfor heating the material in said vessel to maintain the material in aliquid state, and means for heating said wiping means.
 4. Apparatus forcoating fibers with a material in a liquid state, as set forth in claim1, and including means for disabling said material supplying means whenthe material in said vessel is above a predetermined dangerously highlevel, and means for disabling said material supplying means when thematerial in said vessel is below a predetermined dangerously low level.5. Apparatus for coating glass fibers with metal comprising, incombination, a vessel for holding molten metal, means for heating metalin said vessel to a molten state, means for supplying metal to saidvessel at an average rate to maintain a desired surface level for themolten metal, said vessel having a wall with an upper edge spaced belowthe desired surface level for the molten metal, a dam extending upwardlyfrom said upper wall edge and spaced inwardly from an exterior edge ofsaid upper wall edge, said dam having an uppermost edge spaced below andparallel to the desired surface level whereby the molten metal can flowover said dam to form a lip projecting from said exterior edge as aconsequence of the surface tension of the molten metal, a ceramic wiperspaced below and parallel to such lip of molten metal, and means forelectrically heating said wiper to above the melting temperature of themetal whereby, when glass fibers are passed through such lip and oversaid wiper, such fibers are coated with the metal.
 6. Apparatus forcoating glass fibers with metal, as set forth in claim 5, wherein saidvessel includes a concave surface tension recess formed in said vesselparallel to and adjoining said exterior edge, said surface tensionrecess lying between said exterior edge and said wiper to prevent themolten metal from flowing onto said wiper.
 7. Apparatus for coatingglass fibers with metal, as set forth in claim 6, wherein said means forsupplying metal to said vessel includes means for continuouSly feedingwire formed from the metal into said vessel, means for sensing thesurface level of the molten metal in said vessel, and means responsiveto the sensed surface level for controlling the wire feed rate tomaintain the molten metal at substantially the desired surface level. 8.Apparatus for coating glass fibers with metal, as set forth in claim 7,wherein said control means causes said feed means to feed wire at a ratefaster than the metal is normally applied to the fibers when the surfacelevel is below the desired surface level and at a rate slower than themetal is normally applied to the fibers when the surface level is abovethe desired surface level whereby the average wire speed ratecorresponds to the rate at which the metal is applied to the fibers. 9.Apparatus for coating glass fibers with metal, as set forth in claim 8,and including means for disabling said feed means when the deviation ofthe sensed surface level from the desired surface level exceeds apredetermined tolerance.